Electrode having an interphase structure

ABSTRACT

Methods are disclosed for manufacturing an electrode for use in a device such as a secondary battery. Electrodes may include a first layer having first active particles adhered together by a binder, a second layer having second active particles adhered together by a binder, and an interphase layer interposed between the first and second layers. In some examples, the interphase layer may include an interpenetration of the first and second particles, such that substantially discrete fingers of the first layer interlock with substantially discrete fingers of the second layer.

FIELD

This disclosure relates to devices and methods for electrochemicaldevices that include a composite porous electrode. More specifically,disclosed embodiments relate to multilayer electrodes for batteries.

INTRODUCTION

Environmentally friendly sources of energy have become increasinglycritical, as fossil fuel-dependency becomes less desirable. Mostnon-fossil fuel energy sources, such as solar power, wind, and the like,require some sort of energy storage component to maximize usefulness.Accordingly, battery technology has become an important aspect of thefuture of energy production and distribution. Most pertinent to thepresent disclosure, the demand for secondary (i.e., rechargeable)batteries has increased. Various combinations of electrode materials andelectrolytes are used in these types of batteries, such as lead acid,nickel cadmium (NiCad), nickel metal hydride (NiMH), lithium ion(Li-ion), and lithium ion polymer (Li-ion polymer).

SUMMARY

The present disclosure provides systems, apparatuses, and methodsrelating to electrodes having interphase structures, suitable for usewith electrochemical energy storage devices such as supercapacitors,hybrid battery-capacitors, and secondary batteries. Secondary batteriesinclude currently commercialized technologies (e.g., nickel cadmium,Lithium-ion cells) and developing technologies (e.g., fluoride-ion,magnesium-ion, sodium-ion, aluminum-ion).

Features, functions, and advantages may be achieved independently invarious embodiments of the present disclosure, or may be combined in yetother embodiments, further details of which can be seen with referenceto the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an illustrative electrochemicalcell.

FIG. 2 is a magnified view of a portion of the cell of FIG. 1.

FIG. 3 is a schematic side view of an illustrative electrode portion inaccordance with aspects of the present disclosure.

FIG. 4 is a schematic side view of another illustrative electrodeportion in accordance with aspects of the present disclosure.

FIG. 5 is a schematic side view of another illustrative electrodeportion in accordance with aspects of the present disclosure.

FIG. 6 is a schematic side view of another illustrative electrodeportion in accordance with aspects of the present disclosure.

FIG. 7 is a sectional view of an illustrative electrode portion havingan intermediate crust layer on a substantially planar boundary.

FIG. 8 is a sectional view of an illustrative electrode portion havingan interphase layer according to the present teachings.

FIG. 9 is a schematic side view of another illustrative electrodeportion having interlocking fingers in accordance with aspects of thepresent disclosure.

FIG. 10 is a schematic side view of another illustrative electrodeportion having interlocking fingers in accordance with aspects of thepresent disclosure.

FIG. 11 a sectional view of an illustrative electrode portion having aninterphase layer with interlocking fingers according to the presentteachings

FIG. 12 is a flowchart depicting steps of an illustrative method formanufacturing an electrode having an interphase layer in accordance withaspects of the present disclosure.

FIG. 13 is a schematic view of a device suitable for use in the methodof FIG. 12.

DESCRIPTION

Various aspects and examples of an electrode having an interphase layer,as well as related devices and methods, are described below andillustrated in the associated drawings. Unless otherwise specified, anelectrode having an interphase structure as described herein, and/or itsvarious components may, but are not required to, contain at least one ofthe structure, components, functionality, and/or variations described,illustrated, and/or incorporated herein. Furthermore, unlessspecifically excluded, the process steps, structures, components,functionalities, and/or variations described, illustrated, and/orincorporated herein in connection with the present teachings may beincluded in other similar devices and methods, including beinginterchangeable between disclosed embodiments. The following descriptionof various examples is merely illustrative in nature and is in no wayintended to limit the disclosure, its application, or uses.Additionally, the advantages provided by the examples and embodimentsdescribed below are illustrative in nature and not all examples andembodiments provide the same advantages or the same degree ofadvantages.

Definitions

The following definitions apply herein, unless otherwise indicated.

“Substantially” means to be more-or-less conforming to the particulardimension, range, shape, concept, or other aspect modified by the term,such that a feature or component need not conform exactly. For example,a “substantially cylindrical” object means that the object resembles acylinder, but may have one or more deviations from a true cylinder.

“Comprising,” “including,” and “having” (and conjugations thereof) areused interchangeably to mean including but not necessarily limited to,and are open-ended terms not intended to exclude additional, unrecitedelements or method steps.

Terms such as “first”, “second”, and “third” are used to distinguish oridentify various members of a group, or the like, and are not intendedto show serial or numerical limitation.

“Coupled” means connected, either permanently or releasably, whetherdirectly or indirectly through intervening components.

“Secondary battery” means a rechargeable battery, e.g., a type ofelectrical battery which can be charged, discharged by a load, andrecharged multiple times.

Overview

In general, an electrode with interphase structure described herein mayinclude an electrode for use in a bipolar device, e.g., a lithium ionbattery, that includes at least two zones or layers that have differentmicrostructures. In some examples, the layers have different porosities,different materials chemistries, and/or different active materialparticle sizes. In some examples, the electrode has at least one layerwithin which is a gradient of active materials chemistries, a gradientof particle sizes, and/or a multimodal distribution of active materialparticle sizes. As described further below, the two layers may beadhered together via an interphase, which may comprise a non-planartransitional zone between the two layers. In some examples, theinterphase includes a higher concentration of binder molecules.

An electrode having more than one zone or layer may have regions of lowand high porosity, such that the overall electrode has increased energydensity as compared with a homogeneous electrode of an equivalentloading or thickness. By including the interphase, the electrode maymaintain power density and durability (e.g., maintaining mechanicalintegrity during expansion and contraction of the electrode), electronpercolation (i.e., electronically connected), ion conduction, resistanceto solid electrolyte interphase (SEI) buildup, and manufacturing costeffectiveness.

An electrode may have a thickness measured as a distance perpendicularto the plane of a current collector to which the electrode is adhered,between the current collector and an opposing surface of the electrode.The opposing surface (also called the upper surface) may besubstantially planar. This upper surface of the electrode may mate witha separator, a gel electrolyte, or a solid electrolyte when theelectrode is included in a cell. In some examples, an electrodeincluding the interphase of the present disclosure may have a thicknessbetween 20 μm and 1 mm.

Examples, Components, and Alternatives

The following sections describe selected aspects of exemplary deviceshaving electrodes with interphase structures as well as related systemsand/or methods. The examples in these sections are intended forillustration and should not be interpreted as limiting the entire scopeof the present disclosure. Each section may include one or more distinctembodiments or examples, and/or contextual or related information,function, and/or structure.

A. Illustrative Battery

The present teachings disclose a new bipolar electrochemical device(e.g., a battery or electrochemical cell) and electrodes includedtherein. For example, embodiments disclosed herein may include or besuitable for use in a lithium ion battery cell.

Referring now to FIG. 1, a lithium ion battery cell 100 is illustrated,which includes two electrodes, a negative electrode (also known as ananode 102) and a positive electrode (also known as a cathode 104).Current collectors 106, 108, which may comprise metal foils or othersuitable substrates, are electrically coupled to the two electrodes. Thecurrent collectors enable the flow of electrons, and thereby electricalcurrent, into and out of each electrode. An electrolyte 110 enables thetransport of ions between the electrodes 102, 104. In the presentexample, electrolyte 110 is a liquid with dissolved ions thatfacilitates an ionic connection between electrodes 102 and 104.

Electrolyte 110 is typically assisted by a separator 112, whichphysically partitions the space between the cathode and anode whilebeing liquid permeable and enabling the flow of ions within electrolyte110 and between each electrode. In some embodiments, a polymer gel orsolid ion conductor augments or takes the place of (and performs thefunction of) the separator.

The electrodes themselves are composite structures, which compriseactive material particles, a binder, a conductive additive, and pores(void space) for the electrolyte to penetrate. An arrangement ofconstituent parts of an electrode is referred to as a microstructure ormore specifically, an electrode microstructure.

The binder is typically a polymer, e.g., polyvinylidene difluoride(PVdF), and the conductive additive typically includes a nanometer-sizedcarbon, e.g., carbon black, or graphite. In some examples, the binder isa mixture of carboxyl-methyl cellulose (CMC) and styrene-butadienerubber (SBR). In some examples, the conductive additive includes aketjen black, a graphitic carbon, a low dimensional carbon (e.g., carbonnanotubes), or a carbon fiber.

The chemistry of the active material particles differ between anode 102and cathode 104. For example, the anode may include graphite, Titanate,titania, transition metals in general, elements in group 14 (e.g.,carbon, silicon, tin, germanium, etc.), oxides, sulfides, transitionmetals, halides, and chalcogenides. The cathode may include transitionmetals (for example, nickel, cobalt, manganese, copper, zinc, vanadium,chromium, iron), and their oxides, phosphates, phosphites, andsilicates. The cathode may also include alkalines and alkaline earthmetals, aluminum, aluminum oxides and aluminum phosphates, as well ashalides and chalcogenides. In an electrochemical device, activematerials participate in an electrochemical reaction or process with aworking ion (in lithium-ion batteries, lithium ions are the workingions) to store or release energy.

In the present example, during operation of a lithium ion battery,lithium ions move between being included in the active materialparticles and being solvated in the electrolyte. The mass of activematerial divided by the total mass of an electrode (or a cell) is knownas the active material fraction. The volume of active material dividedby the total volume of an electrode (or a cell) is known as the activevolume fraction.

FIG. 2 shows a magnified portion of cell 100. In this example, which isnot the case in other such batteries, the electrode is layered, with afirst layer 114, a second layer 116, and an intermediate interphaselayer 118. Each of these structures is described in further detailbelow.

B. Illustrative Electrode Layer Structures

Three challenges exist in battery technologies: enabling devices with(1) higher energy density, (2) higher power density, and (3) lower costthan those currently available.

The energy density and power density of an electrochemical cell are theresult of a complex interplay of physical and electrochemical propertiesof the cell, including electrochemical and physical properties of theelectrodes, the separator, the current collector, and the electrolyte.

Electrodes are the energy storing components of an electrochemicalenergy storage device (e.g., a lithium-ion battery or a supercapacitor), and are often a composite structure made of active materialparticles and electrically conductive particles embedded in a polymericbinder matrix, as described above.

Physical properties that determine the electrical and electrochemicalperformance of electrodes include: average size (e.g., volume) and sizedistributions of the active material particles, shapes and morphology ofthe active particles, electrode porosity, electrode thickness, activemass fraction, and the method and efficacy of current collection (withinthe electrode and from the electrode to an external circuit). Theseparameters may be extensively tailored to reduce electrode impedance andincrease cell performance.

A major factor affecting the energy density of an electrode (and thus ofan electrochemical energy storage device) is the electrode active massloading. The greater the active mass loading of an electrode, the higherthe electrode's energy storage capacity. Accordingly, a first strategyto improve device energy density is to use a high active mass loading(i.e., high capacity) electrode. This first strategy is effective atincreasing a cell's energy density by increasing a mass (or volume) ofactive material, compared to a mass (or volume) of inactive components(e.g., current collector, separator). An increase in an active massfraction (or equivalently an active volume fraction) of a packaged cellmay be achieved in this way. In addition, higher active mass loadingelectrodes lead to a reduction in cell costs per unit energy. A secondstrategy to improve energy density is to increase an active materialfraction by dense packing of active material particles (for example, ina given volume).

However, both of these strategies may have undesired consequences thatlimit other aspects of cell performance. For example, an increase in theactive mass loading without increasing density increases a thickness ofan electrode. Increasing the thickness of an electrode can adverselyaffect power performance. Typically, a battery electrode is manufacturedby coating a uniform single layer of a slurry on a current collectorsubstrate. As the thickness of the electrode increases, the distancebetween active material particles which are farthest from the currentcollector and the current collector itself increases. As oneconsequence, the length of a path that an electron must take to get tothe active materials particles farthest from the current collector isincreased. As another consequence, the path that an ion must travel froma location outside the electrode to an active material particle locatedclose to the current collector also increases. Thus, increasingelectrode thicknesses leads to increased ohmic resistance and reducedionic conductivity across the thickness of the electrode. Since a powerdensity of an electrode is related to ionic and electronic transportbetween electrode and electrolyte, a reduction in these conductivitiesreduces the power density, resulting in an inverse relationship betweenthe electrode thickness and power density of a battery.

Similarly, there are adverse effects observed when a packing density ofactive material particles is increased. For example, an increase inpacking density may decrease the void space in an electrode, resultingin a less-connected network of void space. As a consequence, a length ofa path that an ion must take to get to a surface of a given activematerial particle may be more tortuous (and therefore longer), comparedto a length of a path an ion may take in a more porous electrode. Inthis way, increasing packing density may reduce ionic conductivitywithin the electrode, adversely affecting power density.

Additionally, in a typical example, the density of active material andthe porosity of the microstructure are uniform throughout an electrode.By packing active material particles closely together and/or makingelectrodes very thick, concentration gradients of lithium ions may buildup within the composite electrode pores when a device is operated at afast rate (e.g., rapid charging or discharging). This phenomenon isknown as polarization and limits rate performance (and thus powerdensity) in a device. Based on all of these considerations, there istypically a clear trade-off between energy density and power densitywhen designing a cell.

A maximum thickness of battery electrodes is generally limited to 100microns for most current applications. Increasing this maximum thicknessto 200 microns or more is understood to increase volumetric andgravimetric energy densities by up to 35%. Increasing electrodethicknesses and/or densities of electrodes are also understood to havemajor impacts on the economics of battery manufacturing, packaging, andend use in multiple applications ranging from consumer electronics totransportation and grid storage. It would be highly advantageous todesign an electrode with structures to mitigate or overcome a trade-offbetween energy density and power.

Significant advances have been made, but existing solutions fall shortin solving these problems. To at least partially address thesechallenges, electrodes with non-uniform microstructure have beenproposed. In one example, an electrode includes at least two layers withdiffering microstructures (e.g., different active materials, porosity,particle size distributions). These layers may further include acontinuous variation in microstructure over a layer. However, solutionsinvolving the formation and properties of an interphase have largelybeen ignored.

Operation of an energy storage device under demanding conditions at thelimits of an electrode's capabilities requires accommodating stressesinduced by volume expansion (swelling) and contraction during thecharging and discharging of battery electrodes. This leads to fourinterrelated challenges. In a first case, a mechanical integrity(coherence) of the electrode must be maintained so that a firstelectrode layer and a second electrode layer remain adhered to eachother (i.e., mechanically stable). In a second case, the first layer andthe second layer must remain electronically connected (percolated),enabling the flow of electrons from the first layer to the second andvice versa. In a third case, the interface between the layers should notblock or inhibit the flow of ions, which would create electrolytepolarization between the layers. In a fourth case, specifically foranodes, the interface between the layers should not create regions ofincreased densification, resulting in solid electrolyte interphase (SEI)buildup at the interface between the layers that subsequently blockspores and induces lithium plating. These issues present a majorchallenge in making a multilayer electrode with high performance bycontrolling a mating between two discrete layers.

The present disclosure provides structures and devices for achievingnon-uniform (e.g., gradient) electrode microstructures, and thusincreased energy density, without decreasing power density. FIG. 3schematically depicts an illustrative electrode portion 300 comprisingtwo active material composite zones or layers 302 and 304. The activematerial composite layers may be adjacent layers, with each lying in aplane generally parallel to a current collector to which the electrodeis adhered. Planes perpendicular to the current collector may lie in thedirection indicated at 320, such that active material composite layers302, 304 are generally parallel to a second direction 322 as well as adirection going into and out of the page of the drawing.

In the present example, first active material composite layer 302 isfarther from the current collector, and closer to a separator and secondactive material composite layer 304 is closer to the current collectorand farther from the separator. First active material composite layer302 includes a plurality of first active material particles 340, abinder 342, and a conductive additive. Second active material compositelayer 304 includes a plurality of second active material particles 350,a binder 352, and a conductive additive. Binders 342 and 352 may be thesame or different, either in type or in concentration. The first andsecond conductive additives may be the same or different, either in typeand/or in concentration.

An interphase 310 interpenetrates and binds the two active materialcomposite layers 302 and 304. First active material particles 340include a number of particles having different volumes that form a firstdistribution of sizes. Second active material particles 350 include anumber of particles having different volumes that form a seconddistribution of sizes. The first and second distributions may besubstantially the same or different. One or both distributions may beunimodal or multimodal. The first and second active material particlesmay have average surface areas which are substantially the same ordifferent, or may have distributions of surface areas with modes thatare substantially the same or different. In general, the first pluralityof active material particles 340 and second plurality of active materialparticles 350 can be same or different in chemical composition, type, ormorphology.

Interphase 310 may include a mixture of first and second active materialparticles with an increased concentration of first active materialparticles, or it may include increased concentration of second activematerial particles. Interphase 310 may have same composition as thefirst layer or the second layer or may have a composition that is amixture of first and second layer composition.

Interphase 310 in the present example includes an increasedconcentration of binder molecules 312 in comparison to first compositezone 302 and/or second composite zone 304. In some examples, interphase310 includes an increased concentration of conductive additive moleculesand conductive additive particles in comparison to first composite zone302 and/or second composite zone 304. For example, interphase 310 maycomprise carbon black, graphitic carbons, amorphous carbons, lowdimensional carbon nanostructures, such as graphene, single-walledcarbon nanotubes, multi-walled carbon nanotubes, bucky balls, transitionmetal and metalloid particles and complexes, and/or the like.

Additionally, these additives may include chemical groups,functionalities, moieties or residues that conduct lithium to improveionic conduction between first zone 302 and second zone 304. Theseadditives may include chemical groups, functionalities, moieties orresidues that conduct electrons to improve electronic conduction betweenthe first zone and the second zone. In further examples, a first workfunction of the first active material particles may be substantiallydifferent from a second work function of the second active materialparticles.

In this example, interphase 310 may include a conductive additive with athird work function between the first and second work functions.Accordingly, interphase 310 may reduce electrical impedance between thefirst and second pluralities. In some examples, interphase 310 includesan increased concentration of binder and an increased concentration ofconductive additive, in comparison to first composite zone 302 and/orsecond composite zone 304. For the purposes of the present disclosure, abinder may include those typically known in the art (e.g., PVdF, CMC,SBR) and additional long chain polymeric chemical species, as well ascombinations and permutations of polymers, and other long-chainmolecules, and/or the like.

In one example, electrode portion 300 is a portion of a cathode includedin a lithium ion cell. In this example during charging of the lithiumion cell, first active material particles 340 and second active materialparticles 350 delithiate. During this process, the active materialparticles may contract, causing electrode portion 300 (as well as theelectrode as a whole) to contract. In contrast, during discharging ofthe cell, the active material particles lithiate and swell, causingelectrode portion 300 and the electrode as a whole to swell.

In an alternate example, electrode portion 300 is a portion of an anodeincluded in a lithium ion cell. In this example, during charging of thelithium ion cell, first active material particles 340 and second activematerial particles 350 lithiate. During this process, the activematerial particles may swell, causing electrode portion 300 (as well asthe electrode as a whole) to swell. In contrast, during discharging ofthe cell, active material particles 340 and 350 delithiate and contract,causing contraction of the electrode.

In either of these examples, during swelling and contracting, electrodeportion 300 may remain coherent, and the first electrode zone and thesecond electrode zone remain bound by interphase 310. In general, theincreased concentration of the binder and/or conductive additive,relative to the concentration of these constituents in first and/orsecond electrode zones 302 and 304, function to adhere the two zonestogether.

In some examples, interphase 310 may include an electrolyte bufferlayer. In one example, a binder or additive molecule is included ininterphase 310 having a porous structure such that it readily adsorbselectrolyte solvent and/or ions. In another example, a mass of afunctionalized molecule, such as a binder or additive is included ininterphase 310 where the functionalized molecule includes a group,moiety, or residue which interacts with electrolyte solvent or ions toimprove transport of electrolyte into or out of at least one of firstzone, 302, second zone 304, or interphase 310.

FIG. 4 schematically depicts another illustrative electrode portion 400.In the present example, a plurality of first particles 440 in a firstzone or layer 402 has a distribution of volumes which have a smalleraverage than the average volume of a plurality of second particles 450in a second zone or layer 404 (i.e., a smaller average size). In someexamples, first particles 440 have a collective surface area that isgreater than the collective surface area of second particles 450. Theplane lying generally perpendicular to the current collector may lie inthe direction 420, such that the planes parallel to the currentcollector include lines parallel to a second direction 422 as well aslines parallel to those going into and out of the page of the drawing.

In some examples, first particles 440 may be further from the currentcollector, and closer to a separator and second particles 450 may becloser to the current collector and further from the separator. In otherexamples, the opposite is true. The two pluralities of particles 440 and450 interpenetrate and bind together in an interphase layer 410.

In the present example, a mechanical interlocking occurs between firstparticles 440 and second particles 450 within interphase 410, because ofthe difference in volumes between the first and second particles. Themechanical interlocking enhances the cohesion of electrode portion 400.In this way interphase 410 mechanically stabilizes electrode portion 400(and the electrode as a whole) during lithiation and delithiation of theactive material particles 440 and 450.

FIG. 5 schematically depicts another illustrative electrode portion 500.The view of FIG. 5 is cross-sectional, such that a direction 520 issubstantially perpendicular to a current collector and/or a separator,and a direction 522 is substantially parallel to a current collectorand/or a separator. Electrode portion 500 includes a plurality of firstactive particles 540 in a first zone or layer 502 and a plurality ofsecond active particles 550 in a second zone or layer 504, as well as aninterphase 510. Interphase 510 may have a thickness 512 of less thaneight microns in direction 520. In additional examples, thickness 512may be: less than 10 microns; less than 20 microns; less than 40microns; less than 60 microns; and/or less than 80 microns.

In the present example, an average distance 552 between particles 550(in direction 522) is greater nearer first particles 540 (alongdirection 520) than an average distance 558 between those secondparticles 550 disposed farther away from the first particles.Additionally, an average distance 554 between the second particles (indirection 522) is greater toward the first particles (along direction520) than an average distance 556 between those second particlesdisposed farther away from the first particles. In the present example,an average distance 542 between first particles 540 is substantiallysimilar to average distance 552.

The structure of the present example may result from a method of formingan electrode (similar to the method discussed below with respect to FIG.12) that includes coating a second layer of composite onto a first layerof composite. In this example, the first layer is substantiallyhomogeneous in terms of its porosity, prior to the coating of the secondlayer. As a result of coating the second layer, solvent from the secondlayer coating interpenetrates the first layer and causes a swellingwithin the first layer. As a result, an average distance between aplurality of active material particles comprised within the first layerincreases for the portion active material particles disposed closest tothe second layer.

FIG. 6 schematically depicts another illustrative electrode portion 600.As with the examples above, electrode portion 600 includes a pluralityof first active particles 640 in a first zone or layer 602 and aplurality of second active particles 650 in a second zone or layer 604,as well as an interphase 610. In this example, electrode portion 600also includes a plurality of third active material particles 660.Particles 660 are a subset of the second particles. Here, particles 660have been compressed, for example during a calendering process, and havea distorted shape, in comparison to the remainder of second particles650. This layer of crushed or flattened active material forms a planarboundary and may be referred to as a “crust.” Such a boundary may beundesirable in many situations. For example, the crust may reduceinterpenetration or intermixing of the two particle types, such that theinterphase layer is less effective. FIG. 7 is a sectional view of anelectrode 700 in which two such crusts are present. Electrode 700includes a first layer 702 having first particles 704 and a second layer706 having second particles 708, between a current collector 710 at thebottom and a separator 712 at the top. As depicted in FIG. 7, secondparticles 708 have been pressed or calendered, forming a crust 714 at aclear planar boundary between the two layers. A second crust 716 ispresent at the boundary between the first particles and the separator,where the electrode layers were calendered as a whole in preparation foradhering to the separator. As explained throughout this disclosure, thistype of electrode may be less than adequate to withstand the challengesof mechanical integrity, electronic percolation, ionic conduction, andSEI buildup between the two active material composite layers.

FIG. 8 is a sectional view of an illustrative electrode portion 800similar to electrode portions 400 or 500. In this example, activematerials 802 have been layered onto a current collector substrate 804.The active materials comprise a first layer 806 including a plurality offirst active material particles 808 adhered together by a first binder.The first particles have a first average particle size. Active materials802 further comprise a second layer 810 including a plurality of secondactive material particles 812 adhered together by a second binder. Thesecond particles having a second average particle size different thanthe first. In this example, the second particles are smaller than thefirst particles.

Electrode portion 800 also includes an interphase layer 814 adheringfirst layer 806 to second layer 810. In the present example, interphase814 may have a composition substantially similar to first layer 806,second layer 810, or a physical mixture of the two layers. Further, inthe present example interphase 814 may have a binder composition andconcentration substantially similar to first layer 806, second layer810, or a physical mixture of the two layers. Further still, in thepresent example interphase 814 may have a conductive additivecomposition and concentration substantially similar to first layer 806,second layer 810, or a physical mixture of the two layers. Interphaselayer 814 includes an intermixing or interpenetration of the firstparticles and the second particles, such that the interphase layer has athird average particle size smaller than the first average particle sizeand larger than the second average particle size. In other words,interphase layer 814 comprises a gradual transition from the firstparticles of first layer 806 to the second particles of second layer810. A separator 816 is adhered to second layer 810.

FIG. 9 schematically depicts another illustrative electrode portion 900,comprising two active material composite layers 902 and 904. The activematerial composite layers may be adjacent layers, with each lying in aplane generally parallel to a current collector to which the electrodeis adhered. Planes perpendicular to the current collector may lie in thedirection indicated at 920, such that active material composite layers902, 904 are generally parallel to a second direction 922 as well as adirection going into and out of the page of the drawing.

In the present example, first active material composite layer 902 isfarther from the current collector, and closer to a separator, andsecond active material composite layer 904 is closer to the currentcollector and farther from the separator. First active materialcomposite layer 902 includes a plurality of first active materialparticles 940, a binder, and a conductive additive. Second activematerial composite layer 904 includes a plurality of second activematerial particles 950, a binder, and a conductive additive.

An interphase 910 interpenetrates and binds the two active materialcomposite layers 902 and 904. First active material particles 902include a number of particles having different volumes that form a firstdistribution of sizes. Second active material particles 904 include anumber of particles having different volumes that form a seconddistribution of sizes. The first and second distributions may besubstantially the same or different. One or both distributions may beunimodal or multimodal. The first and second active material particlesmay have average surface areas which are substantially the same ordifferent, or may have distributions of surface areas with modes thatare substantially the same or different.

Interphase 910 in the present example includes a non-planar boundarybetween first active material composite layer 902 and second activematerial composite layer 904. First active material composite layer 902and second active material composite layer 904 have respective,three-dimensional, interpenetrating fingers 914 and 916 that interlockthe two active material composite layers together, forming amechanically robust interphase that is capable of withstanding stressesdue to electrode expansion and contraction. Additionally, the non-planarsurfaces defined by first fingers 914 and second fingers 916 representan increased total surface area of the interphase boundary, whichprovides more binding sites between the first active material compositelayer and the second active material composite layer. Fingers 914 and916 may be referred to as fingers, protrusions, extensions, projections,and/or the like. Furthermore, the relationship between fingers 914 and916 may be described as interlocking, interpenetrating, intermeshing,interdigitating, interconnecting, interlinking, and/or the like.

Fingers 914 and fingers 916 are a plurality of substantially discreteinterpenetrations, wherein fingers 914 are generally made up of firstactive material particles 940 and fingers 916 are generally made up ofsecond active material particles 950. The fingers arethree-dimensionally interdigitated, analogous to an irregular form ofthe stud-and-tube construction of Lego bricks. Accordingly, fingers 914and 916 typically do not span the electrode in any direction, such thata cross section perpendicular to that of FIG. 9 will also show anon-planar, undulating boundary similar to the one shown in FIG. 9.Although fingers 914 and 916 may not be uniform in size or shape, thefingers may have an average or typical length 918. In some examples,length 918 of fingers 914 and 916 may fall in a range between two andfive times the average active material particle size of the first activematerial composite layer or the second active material composite layer,whichever is smaller. In some examples, length 918 of fingers 914, 916may fall in a range between six and ten times the average activematerial particle size of the first active material composite layer orthe second active material composite layer, whichever is smaller. Insome examples, length 918 of fingers 914 and 916 may fall in a rangebetween eleven and fifty times the average active material particle sizeof the first active material composite layer or the second activematerial composite layer, whichever is smaller. In some examples, length918 of fingers 914 and 916 may be greater than fifty times the averageactive material particle size of the first active material compositelayer or the second active material composite layer, whichever issmaller.

In some examples, length 918 of fingers 914 and 916 may fall in a rangeof approximately two to approximately five μm. In some examples, length918 of fingers 914 and 916 may fall in a range between approximately sixand approximately ten μm. In another example, length 918 of fingers 914and 916 may fall in a range between approximately eleven andapproximately fifty μm. In another example, length 918 of fingers 914and 916 may be greater than approximately fifty μm.

In the present example, a total thickness 924 of interphase region 910is defined by the level of interpenetration between the two activematerial composite layers. A lower limit 926 may be defined by thelowest point reached by first active material composite layer 902 (i.e.by fingers 914). An upper limit 928 may be defined by the highest pointreached by the second active material composite layer 904 (i.e. byfingers 916). Total thickness 924 of interphase region 910 may bedefined as the separation or distance between limits 926 and 928. Insome examples, the total thickness of interphase region 910 may fallwithin one or more of various relative ranges, such as betweenapproximately 200% (2×) and approximately 500% (5×), approximately 500%(5×) and approximately 1000% (10×), approximately 1000% (10×) andapproximately 5000% (50×), and/or greater than approximately 5000% (50×)of the average active material particle size of the first activematerial composite layer or the second active material composite layer,whichever is smaller.

In some examples, total thickness 924 of interphase region 910 may fallwithin one or more of various absolute ranges, such as betweenapproximately three and approximately ten μm, approximately ten andapproximately fifty μm, approximately fifty and approximately onehundred μm, approximately one hundred and approximately one hundredfifty μm, and/or greater than approximately one hundred fifty μm.

In the present example, first active material particles 940 in firstactive material composite layer 902 have a distribution of volumes whichhave a greater average than an average volume of second active materialparticles 950 in second active material composite layer 904 i.e., alarger average size. In some examples, first active material particles940 have a collective surface area that is less than the collectivesurface area of second active material particles 950. In other examples,the opposite is true. First active material particles 940 have adistribution of volumes which have a smaller average than the averagevolume of second active material particles 950, i.e., a smaller averagesize. In some examples, first active material particles 940 have acollective surface area that is greater than a collective surface areaof second active material particles 950.

In the present example, first active material particles 940 and secondactive material particles 950 are substantially spherical in particlemorphology. In other examples, one or both of the plurality of activematerial particles in either active material composite layer may haveparticle morphologies that are: flake-like, platelet-like, irregular,potato-shaped, oblong, fractured, agglomerates of smaller particletypes, and/or a combination of the above.

When particles of electrode portion 900 are lithiating or delithiating,as explained above with respect to electrode 300, (i.e., during swellingand contracting), electrode portion 900 remains coherent, and the firstactive material composite layer and the second active material compositelayer remain bound by interphase 910. In general, the interdigitation orinterpenetration of fingers 914 and 916, as well as the increasedsurface area of the interphase boundary, function to adhere the twozones together.

FIG. 10 schematically depicts another illustrative electrode portion1000 comprising two active material composite layers 1002 and 1004forming an interphase 1010 having interlocked fingers 1014 and 1016. Theactive material composite layers may be adjacent layers, with each lyingin a plane generally parallel to a current collector to which theelectrode is adhered. Planes perpendicular to the current collector maylie in the direction indicated at 1020, such that active materialcomposite layers 1002 and 1004 are generally parallel to a seconddirection 1022 as well as a direction going into and out of the page ofthe drawing.

In the present example, first active material composite layer 1002 isfarther from the current collector, and closer to a separator, andsecond active material composite layer 1004 is closer to the currentcollector and farther from the separator. First active materialcomposite layer 1002 includes a plurality of first active materialparticles 1040, a binder, and a conductive additive. Second activematerial composite layer 1004 includes a plurality of second activematerial particles 1050, a binder, and a conductive additive.

Electrode 1000 is substantially similar to electrode 900, and in generalmay be described in similar terms. In the present example of FIG. 10,however, first active material particles 1040 in first active materialcomposite layer 1002 are substantially spherical in particle morphology,whereas second active material particles 1050 in second active materialcomposite layer 1004 are spherical, flake-like, platelet-like,irregular, potato-shaped, oblong, fractured, agglomerates of smallerparticle types, or a combination of the above in particle morphology. Inother examples, the opposite may be true.

FIG. 11 is a sectional view of an illustrative electrode portion 1100similar to electrode portions 900 and 1000. In this example, activematerial particles 1102 have been layered onto a current collectorsubstrate 1104. The active materials comprise a first active materialcomposite layer 1106 including a plurality of first active materialparticles 1108 adhered together by a first binder. First active materialparticles 1108 have a first average particle size 1118. Active materialparticles 1102 further comprise a second active material composite layer1110 including a plurality of second active material particles 1112adhered together by a second binder. Second active material particles1112 have a second average particle size 1120, different than the first.In this example, second active material particles 1112 are smaller thanfirst active material particles 1108. In other examples, the opposite istrue.

A substantially non-planar interphase boundary 1114 is disposed betweenfirst active material composite layer 1106 and second active materialcomposite layer 1110. The first active material composite layer hasfingers 1122 extending into the second active material composite layer,and the second active material composite layer has fingers 1124extending into the first active material composite layer. A lower limit1126 and an upper limit 1128 of the interphase region is defined by thelowest point reached by first fingers 1122 and the highest point reachedby second fingers 1124, respectively.

Structures of the FIGS. 9-11 may result from a method of forming anelectrode (such as the method discussed below with respect to FIG. 12)that includes coating a second active material composite slurry onto afirst layer of active material composite slurry. As a result of coatingthe two layers, solvent from the first active material composite slurryand the second active material composite slurry intermix to a limiteddegree, causing interpenetrating finger structures to form.

Although various electrode portions above are shown and described ashaving two active material composite layers coupled by an interphase,electrodes according to the present disclosure may include additionallayers, such as a total of three or four active material compositelayers. Each of the additional layers may be adhered to adjacentlayer(s) by a respective interphase, substantially as described herein.In some examples, each of the interphase layers may be of the same type.In some examples, different interphase types may exist within the sameelectrode (i.e., between different pairs of active material compositelayers).

The examples and embodiments discussed above are not meant to belimiting in any fashion, and may be considered together in a number ofpermutations and combinations. The examples given above include lithiumion batteries, however additional examples and embodiments could be usedfor any electrochemical or bipolar device that has a liquid/solidinterface, gas/solid interface or a solid/solid interface where anelectrolytic media interpenetrates a micro- or nano-structuredelectrode.

C. Illustrative Method

This section describes steps of an illustrative method 1200 for formingan electrode including an interphase; see FIG. 12. Aspects of electrodesand manufacturing devices described herein may be utilized in the methodsteps described below. Where appropriate, reference may be made tocomponents and systems that may be used in carrying out each step. Thesereferences are for illustration, and are not intended to limit thepossible ways of carrying out any particular step of the method.

FIG. 12 is a flowchart illustrating steps performed in an illustrativemethod, and may not recite the complete process or all steps of themethod. Although various steps of method 1200 are described below anddepicted in FIG. 12, the steps need not necessarily all be performed,and in some cases may be performed simultaneously, or in a differentorder than the order shown.

Step 1202 of method 1200 includes providing a substrate. In someexamples, the substrate comprises a current collector, such as currentcollectors 106, 108 (and others) described above. In some examples, thesubstrate comprises a metal foil.

Method 1200 next includes a plurality of steps in which at least aportion of the substrate is coated with an active material composite.This may be done by causing the substrate to move past an activematerial composite dispenser (or vice versa) that coats the substrate asdescribed below.

Step 1204 of method 1200 includes coating a first layer of a compositeelectrode on a first side of the substrate. In some examples, the firstlayer may include a plurality of first particles adhered together by afirst binder, the first particles having a first average particle size.

The coating process of step 1204 may include any suitable coatingmethod(s), such as slot die, blade coating, spray-based coating,electrostatic jet coating, or the like. In some examples, the firstlayer is coated as a wet slurry of solvent (water, or NMP), binder,conductive additive, and active material. In some examples, the firstlayer is coated dry, as an active material with a binder and/or aconductive additive. Step 1204 may optionally include drying the firstlayer of the composite electrode.

Step 1206 of method 1200 includes coating a second layer of a compositeelectrode, on the first side of the substrate, onto the first layer,forming a multilayered (e.g., stratified) structure. The second layermay include a plurality of second particles adhered together by a secondbinder, the second particles having a second average particle size.

Step 1208 of method 1200 includes forming an interphase layer adheringthe first layer to the second layer. Forming this interphase layer maybe done by causing an interpenetration of the second layer into thefirst layer. This may result in an increased or decreased concentrationof a binder and/or a conductive additive. Where the first layer andsecond layer contain different particle sizes, the interphase layerincludes an intermixing of the first particles and the second particles,such that there is an interlocking of the first particles of the firstlayer to the second particles of the second layer.

In some examples, step 1208 occurs concurrent or immediately followingstep 1206. When these examples include drying the first layer of thecomposite electrode, a rewetting of the first layer occurs during step1206 (coating the second layer onto the first layer). Rewetting of thefirst layer results in a gradient of porosity between active materialparticles within the first layer and/or active material particles withinthe interphase. Alternatively, rewetting of the first layer by thesolvent from the second layer re-solvates the binder in the first layerto create an intermixing of first active material particles and secondactive material particles, resulting in the formation ofinterpenetrating fingers.

In some examples, forming an interphase in step 1208 comprises anadditional deposition or coating of material onto the first layer, priorto the coating of the second layer. For example, a third type of bindermay be deposited onto the first layer.

In some examples, steps 1204 and 1206 may be performed substantiallysimultaneously, such that the interphase of step 1208 is formed asinterpenetrating fingers (e.g., fingers 914, 916). These fingers areformed by extruding both of the active material slurries through theirrespective orifices simultaneously. This forms a two-layer slurry beadand coating on the moving substrate. Difference in viscosities,difference in surface tensions, difference in densities, difference insolids contents, and/or different solvents used between the first activematerial slurry and the second active material slurry may be tailored tocause interpenetrating finger structures at the boundary between the twoactive material composite layers. In some embodiments, the viscosities,surface tensions, densities, solids contents, and/or solvents may besubstantially similar. Creation of interpenetrating structures isfacilitated by turbulent flow at the wet interface between the firstactive material electrode slurry and the second active materialelectrode slurry, creating partial intermixing of the two activematerial electrode slurries.

Too much intermixing between the two active material electrode slurriesmay result in the loss of a functional gradient in the resulting driedelectrode composite, whereas too little intermixing between the twoactive material electrode slurries may result in a less-preferred,substantially planar interphase boundary. Additionally, to ensure propercuring in the drying process, the first layer (closest to the currentcollector) is configured to be dried from solvent prior to the secondlayer (further from the current collector) so as to avoid creatingskin-over effects and blisters in the resulting dried coatings.

In general, the first active material composite slurry will have a firstviscosity and the second active material composite slurry will have asecond viscosity different than the first. In some examples, adifference in viscosities between the first active material electrodeslurry and the second active material electrode slurry is targeted to be100-1,000 centipoise (cP). In other examples, a difference inviscosities between the first active material electrode slurry and thesecond active material electrode slurry is targeted to be 2,000-5,000cP. In other examples, a difference in viscosities between the firstactive material electrode slurry and the second active materialelectrode slurry is targeted to be 6,000-10,000 cP. In other examples, adifference in viscosities between the first active material electrodeslurry and the second active material electrode slurry is targeted to begreater than 10,000 cP.

In some examples, a difference in surface tensions between the firstactive material electrode slurry and the second active materialelectrode slurry is targeted to be 0.5-1 dynes/cm. In other examples, adifference in surface tensions between the first active materialelectrode slurry and the second active material electrode slurry istargeted to be 1-5 dynes/cm. In other examples, a difference in surfacetensions between the first active material electrode slurry and thesecond active material electrode slurry is targeted to be 6-10 dynes/cm.In other examples, a difference in surface tensions between the firstactive material electrode slurry and the second active materialelectrode slurry is targeted to be greater than 10 dynes/cm.

In some examples, a difference in densities between the first activematerial electrode slurry and the second active material electrodeslurry is targeted to be 0.01-0.1 g/cc. In other examples, a differencein densities between the first active material electrode slurry and thesecond active material electrode slurry is targeted to be 0.2-0.5 g/cc.In other examples, a difference in densities between the first activematerial electrode slurry and the second active material electrodeslurry is targeted to be 0.5-1 g/cc. In other examples, a difference indensities between the first active material electrode slurry and thesecond active material electrode slurry is targeted to be greater than 1g/cc.

In some examples, a difference in solids content between the firstactive material electrode slurry and the second active materialelectrode slurry is targeted to be 0.25%-1%. In other examples, adifference in solids contents between the first active materialelectrode slurry and the second active material electrode slurry istargeted to be 2%-5%. In other examples, a difference in solids contentsbetween the first active material electrode slurry and the second activematerial electrode slurry is targeted to be 6%-10%. In other examples, adifference in solids contents between the first active materialelectrode slurry and the second active material electrode slurry istargeted to be greater than 10%.

In some examples, the solvent(s) used in the first or second activematerial electrode slurry may consist of one or more solvents from groupconsisting of water, dimethylformamide, ethanol, propanol, propan-2-ol,butanol, 2-methylpropan-1-ol, N-Methyl-2-pyrrolidone, dimethylsulfoxide,diethyl ether, dimethyl ether and ethyl methyl ether.

Method 1200 may optionally include drying the composite electrode instep 1210, and calendering the composite electrode in step 1212. Inthese optional steps, both the first and second layers may experiencethe drying process and the calendering process as a combined structure.In some examples, steps 1210 and 1212 may be combined (e.g., in a hotroll process). In some examples, drying step 1210 includes a form ofheating and energy transport to and from the electrode (e.g.,convection, conduction, radiation) to expedite the drying process. Insome examples, calendering step 1212 is replaced with anothercompression, pressing, or compaction process. In some examples,calendering the electrode may be performed by pressing the combinedfirst and second layers against the substrate, such that electrodedensity is increased in a non-uniform manner, with the first layerhaving a first porosity and the second layer having a lower secondporosity.

D. Illustrative Dispenser Device

This section describes an illustrative system 1300 suitable for use withmethod 1200. In some examples, a slot-die coating head with at least twofluid slots, fluid cavities, fluid lines, and fluid pumps may be used tomanufacture a battery electrode featuring at least one interpenetratingboundary layer between active material composite layers. In someexamples, a dual-cavity slot-die coating head is used to manufacture abattery electrode featuring one interpenetrating boundary layer betweentwo active material composite layers. In some examples, a triple-cavityslot-die coating head is used to manufacture a battery electrodefeaturing two interpenetrating boundary layers disposed between threeactive material composite layers. In other examples, additional cavitiesare used to create additional layers. System 1300 includes a dual-cavityslot-die coating head.

System 1300 is a manufacturing system in which a foil substrate 1302(e.g., current collector substrate 804) is transported by a revolvingbacking roll 1304 past a stationary dispenser device 1306. Dispenserdevice 1306 may include any suitable dispenser configured to evenly coatone or more layers of active material slurry onto the substrate, asdescribed with respect to steps 1204 and 1206 of method 1200. In someexamples, the substrate may be held stationary while the dispenser headmoves. In some examples, both may be in motion.

Dispenser device 1306 may, for example, include a dual chamber slot diecoating device having a coating head 1308 with two orifices 1310 and1312. A slurry delivery system supplies two different active materialslurries to the coating head under pressure. Due to the revolving natureof backing roll 1304, material exiting the lower orifice or slot 1310will contact substrate 1302 before material exiting the upper orifice orslot 1312. Accordingly, a first layer 1314 will be applied to thesubstrate and a second layer 1316 will be applied on top of the firstlayer.

Accordingly, corresponding steps of method 1200 may be characterized asfollows. Causing a current collector substrate and an active materialcomposite dispenser to move relative to each other, and coating at leasta portion of the substrate with an active material composite, using thedispenser. Coating, in this case, includes: applying a first layer ofslurry to the substrate using a first orifice or slot of the dispenser,and applying a second layer of a different slurry to the first layerusing a second orifice or slot of the dispenser. These steps cause aninterphase layer to form, thereby adhering the first layer to the secondlayer. As described above, based on different characteristics betweenthe two slurries, the interphase layer may include an interpenetrationof the first and second layers in which first fingers of the first layerinterlock with second fingers of the second layer.

E. Additional Examples and Illustrative Combinations

This section describes additional aspects and features of electrodeshaving interphase structures, and related methods, presented withoutlimitation as a series of paragraphs, some or all of which may bealphanumerically designated for clarity and efficiency. Each of theseparagraphs can be combined with one or more other paragraphs, and/orwith disclosure from elsewhere in this application (including theclaims), in any suitable manner. Some of the paragraphs below expresslyrefer to and further limit other paragraphs, providing withoutlimitation examples of some of the suitable combinations.

A0. An electrode comprising:

a current collector substrate; and

an active material composite layered onto the substrate, wherein theactive material composite comprises:

-   -   a first layer including a plurality of first active material        particles adhered together by a first binder, the first active        material particles having a first average particle size;        -   a second layer including a plurality of second active            material particles adhered together by a second binder, the            second active material particles having a second average            particle size; and        -   an interphase layer adhering the first layer to the second            layer, the interphase layer including an intermixing of the            first active material particles and the second active            material particles, such that the interphase layer has a            third average active material particle size, a magnitude of            which is between the first average active material particle            size and the second average active material particle size.

A1. The electrode of A0, wherein the interphase further comprises athird binder adhering the first active material particles to the secondactive material particles, wherein the third binder has a higherconcentration than the first binder and the second binder.

A2. The electrode of A0, wherein the active material composite comprisesa first face in direct contact with the current collector substrate anda second face opposite the first face, the second face in contact with aseparator.

A3. The electrode of A0, wherein the interphase layer comprises anintermixing of the first active material particles and the second activematerial particles, such that the interphase layer comprises a gradualtransition from the first active material particles of the first layertransition to the second active material particles of the second layer.A4. The electrode of A0, wherein the interphase layer comprises aplurality of fluid passages defined at least in part by the first activematerial particles and the second active material particles.

A5. The electrode of A4, wherein the plurality of fluid passages arefurther defined by a plurality of conductive additive particles.

A6. A secondary battery comprising the electrode of A0.

A7. The electrode of A0, wherein the electrode is an anode, and thefirst particles comprise a graphitic carbon.

A8. The electrode of A7, wherein the second particles comprise carbon.

B0. An electrode comprising:

a current collector substrate; and

an active material composite layered onto the substrate, wherein theactive material composite comprises:

-   -   a first layer including a plurality of first active material        particles adhered together by a first binder, the first active        material particles having a first average particle size;    -   a second layer including a plurality of second active material        particles adhered together by a second binder, the second active        material particles having a second average particle size; and    -   an interphase layer adhering the first layer to the second        layer, the interphase layer including an intermixing of the        first active material particles and the second active material        particles, such that the interphase layer comprises a gradual        transition from the first active material particles of the first        layer to the second active material particles of the second        layer.

B1. The electrode of B0, wherein the interphase further comprises athird binder adhering the first active material particles to the secondactive material particles.

B2. The electrode of B0, wherein the active material composite comprisesa first face in direct contact with the current collector substrate anda second face opposite the first face, the second face in contact with aseparator.

B3. The electrode of B0, wherein the interphase layer comprises anintermixing of the first active material particles and the second activematerial particles, such that the interphase layer has a third averageactive material particle size intermediate the first average activematerial particle size and the second average active material particlesize.

B4. The electrode of B0, wherein the interphase layer comprises aplurality of fluid passages defined at least in part by the first activematerial particles and the second active material particles.

B5. The electrode of B4, wherein the plurality of fluid passages arefurther defined by a plurality of conductive additive particles.

C0. A method of manufacturing an electrode, the method comprising:

causing a current collector substrate and an active material compositedispenser to move relative to each other; and

-   -   coating at least a portion of the substrate with an active        material composite, using the dispenser, wherein coating        includes:        -   applying a first layer to the substrate using a first            orifice of the dispenser, the first layer including a            plurality of first active material particles and a first            binder, the first active material particles having a first            average particle size;        -   applying a second layer to the first layer using a second            orifice of the dispenser, the second layer including a            plurality of second active material particles and a second            binder, the second active material particles having a second            average particle size; and        -   forming an interphase layer adhering the first layer to the            second layer, the interphase layer including an intermixing            of the first active material particles and the second active            material particles, such that the interphase layer comprises            a gradual transition from the first active material            particles of the first layer to the second active material            particles of the second layer.

C1. The method of C0, wherein the interphase layer comprises anintermixing of the first active material particles and the second activematerial particles, such that the interphase layer has a third averageactive material particle size sized between the first average activematerial particle size and the second average active material particlesize.

C2. The method of C0, wherein causing the substrate and the dispenser tomove relative to each other comprises moving the substrate using abackup roll.

C3. The method of C0, wherein the dispenser comprises a dual chamberslot die coating head, such that the first orifice is a first slot ofthe coating head and the second orifice is a second slot of the coatinghead.

C4. The method of C0, further comprising drying the first layer prior toapplying the second layer.

C5. The method of C0, further comprising:

calendering the electrode by pressing the combined first and secondlayers against the substrate, increasing an overall density of theelectrode and decreasing an overall porosity of the electrode.

D0. An electrode comprising:

a current collector substrate; and

an active material composite layered onto the substrate, wherein theactive material composite comprises:

-   -   a first layer including a plurality of first active material        particles adhered together by a first binder, the first active        material particles having a first average particle size;    -   a second layer including a plurality of second active material        particles adhered together by a second binder, the second active        material particles having a second average particle size; and    -   an interphase layer adhering the first layer to the second        layer, the interphase layer including a non-planar boundary        between the first and second layers, such that the first layer        and the second layer are interpenetrated and the interphase        layer has a third average particle size, a magnitude of which is        between the first average particle size and the second average        particle size.

D1. The electrode of D0, the non-planar boundary comprising a pluralityof substantially discrete first fingers of the first active materialparticles interlocked with a plurality of substantially discrete secondfingers of the second active material particles.

D2. The electrode of D1, wherein the first fingers each have a lengthgreater than approximately two times the smaller of the first averageparticle size and the second average particle size.

D3. The electrode of D0, wherein the first layer comprises a first facein direct contact with the current collector substrate and the secondlayer has a second face in direct contact with a separator (e.g., thesecond face is on an opposite side of the active material composite fromthe first face).

D4. The electrode of D0, wherein the interphase layer comprises aplurality of fluid passages defined at least in part by the first activematerial particles and the second active material particles.

D5. The electrode of D4, wherein the plurality of fluid passages arefurther defined by a plurality of conductive additive particles.

D6. A secondary battery comprising the electrode of D0.

D7. The electrode of D0, wherein the electrode is an anode, and thefirst active material particles comprise carbon.

E0. An electrode comprising:

a current collector substrate; and

an active material composite layered onto the substrate, wherein theactive material composite comprises:

-   -   a first layer including a plurality of first active material        particles having a first distribution of particle sizes;    -   a second layer including a plurality of second active material        particles having a second distribution of particle sizes; and    -   an interphase layer adhering the first layer to the second        layer, the interphase layer including a non-planar        interpenetration of the first and second layers in which first        fingers of the first layer interlock with second fingers of the        second layer.

E1. The electrode of E0, wherein the first fingers each have a lengthgreater than approximately two microns.

E2. The electrode of E0, wherein the first layer has a first face indirect contact with the current collector substrate and the second layerhas a second face in direct contact with a separator (e.g., the secondface and the first face are on opposing sides of the active materialcomposite).

E3. The electrode of E0, wherein the first layer has a first porosity,the second layer has a different second porosity, and the interphaselayer has a third porosity intermediate the first porosity and thesecond porosity.

E4. The electrode of E0, wherein the interphase layer comprises aplurality of fluid passages defined at least in part by the firstparticles and the second particles.

E5. A secondary battery comprising the electrode of E0.

F0. A method of manufacturing an electrode, the method comprising:

causing a current collector substrate and an active material compositedispenser to move relative to each other; and

coating at least a portion of the substrate with an active materialcomposite, using the dispenser, wherein coating includes:

-   -   applying a first layer to the substrate using a first orifice of        the dispenser, the first layer including a first active material        composite slurry having a plurality of first active material        particles and a first binder, the first active material        particles having a first average particle size and a first        viscosity;    -   applying a second layer to the first layer using a second        orifice of the dispenser, the second layer including a second        active material composite slurry having a plurality of second        active material particles and a second binder, the second active        material particles having a second average particle size and a        second viscosity; and    -   forming an interphase layer adhering the first layer to the        second layer, the interphase layer including an interpenetration        of the first and second layers in which first fingers of the        first layer interlock with second fingers of the second layer.

F1. The method of F0, wherein the interphase layer has a third averageactive material particle size between the first average active materialparticle size and the second average active material particle size.

F2. The method of F0, wherein causing the substrate and the dispenser tomove relative to each other comprises moving the substrate using abackup roll.

F3. The method of F0, wherein the dispenser comprises a dual chamberslot die coating head, such that the first orifice is a first slot ofthe coating head and the second orifice is a second slot of the coatinghead.

F4. The method of F0, wherein the first viscosity and the secondviscosity differ by at least one hundred centipoise (cP).

F5. The method of F0, further comprising:

calendering the electrode by pressing the combined first and secondlayers against the substrate, such that an electrode density isincreased in a non-uniform manner, the first layer having a firstporosity and the second layer having a second porosity less than thefirst porosity.

G0. The electrode of D0, E0, or F0, including fingers comprising domainsof first particles interlocking with domains of second particles.

G1. The electrode of D0, E0, or F0, wherein the boundary of theinterphase has a surface area that is at least twice as large as wouldbe a substantially planar boundary between the first layer and thesecond layer.

G2. The electrode of D0, E0, or F0, wherein the first layer comprises afirst homogeneous structure having a first porosity, and the secondlayer comprises a second homogeneous structure having a second porositydifferent than the first porosity.

Advantages, Features, Benefits

The different embodiments and examples of electrode structures andrelated methods described herein provide several advantages over knownsolutions. For example, illustrative embodiments and examples describedherein facilitate improved ionic communication over examples having asubstantially planar inter-layer boundary. Interphase layers of thepresent disclosure provide improved mechanical integrity, electricalcommunication, ionic conduction, and resistance to SEI buildup, as theinterpenetration and interlocking of active material composite layerslowers impedance between the two layers.

Additionally, and among other benefits, illustrative embodiments andexamples described herein have interphase layers comprising a network offluid passageways defined by active material particles, binder, and/orcarbon additive. These fluid passages are not hampered bycalendering-induced changes in mechanical or morphological state of theparticles. In contrast, a substantially planar boundary is oftenassociated with the formation of a crust layer upon subsequentcalendering. Such a crust layer is disadvantageous for electronicpercolation, as described above, and also serves to significantly impedeion conduction through the interphase region. This increases thetortuosity of the overall electrode as ions face a barrier within theelectrode composite as they traverse through the thickness of theelectrode, causing the power density of the battery to suffersignificantly. Furthermore, such a crust layer also represents alocalized compaction of active material particles that effectivelyresult in reduced pore volumes; this may be an issue of particularimportance for anode electrodes. Further in the case of anodeelectrodes, SEI film buildup on active material particles clogs thepores at a quicker rate, leading to increased cell polarization andlithium plating, ultimately leading to poor cycle life and compromisedsafety.

Additionally, and among other benefits, illustrative embodiments andexamples described herein provide improved electrical communication, asthe interpenetration or intermixing of active materials and conductiveadditives lowers impedance between the two layers.

Additionally, and among other benefits, illustrative embodiments andexamples described herein allow improved mechanical coherence of theelectrode. Peel strength is such that the two layers do notpreferentially separate at the interphase.

Additionally, and among other benefits, illustrative embodiments andexamples described herein provide improved mechanical integrity of theelectrode structure sufficient to accommodate the stresses induced byvolume expansion and contraction during the charging and dischargingprocesses when assembled into a battery, improving cycle life of thebattery.

Additionally, and among other benefits, illustrative embodiments andexamples described herein provide a non-planar boundary between the twoactive material composite layers, such that the active materialparticles of the first active material composite layer will haveimproved electronic percolation with the active material particles ofthe second active material composite layer, and vice versa, resulting inreduced impedance for the overall electrode and cell.

No known system or device can perform these functions. However, not allembodiments and examples described herein provide the same advantages orthe same degree of advantage.

CONCLUSION

The disclosure set forth above may encompass multiple distinct exampleswith independent utility. Although each of these has been disclosed inits preferred form(s), the specific embodiments thereof as disclosed andillustrated herein are not to be considered in a limiting sense, becausenumerous variations are possible. To the extent that section headingsare used within this disclosure, such headings are for organizationalpurposes only. The subject matter of the disclosure includes all noveland nonobvious combinations and subcombinations of the various elements,features, functions, and/or properties disclosed herein. The followingclaims particularly point out certain combinations and subcombinationsregarded as novel and nonobvious. Other combinations and subcombinationsof features, functions, elements, and/or properties may be claimed inapplications claiming priority from this or a related application. Suchclaims, whether broader, narrower, equal, or different in scope to theoriginal claims, also are regarded as included within the subject matterof the present disclosure.

What is claimed is:
 1. An electrode comprising: a current collectorsubstrate; and an active material composite layered onto the substrate,wherein the active material composite comprises: a first layer includinga plurality of first active material particles adhered together by afirst binder, the first active material particles having a first averageparticle size; a second layer including a plurality of second activematerial particles adhered together by a second binder, the secondactive material particles having a second average particle size; and aninterphase layer adhering the first layer to the second layer, theinterphase layer including a non-planar boundary between the first andsecond layers, such that the first layer and the second layer areinterpenetrated and the interphase layer has a third average particlesize between the first average particle size and the second averageparticle size.
 2. The electrode of claim 1, the non-planar boundarycomprising a plurality of substantially discrete first fingers of thefirst active material particles interlocked with a plurality ofsubstantially discrete second fingers of the second active materialparticles.
 3. The electrode of claim 2, wherein the first fingers eachhave a length greater than approximately two times the smaller of thefirst average particle size and the second average particle size.
 4. Theelectrode of claim 1, wherein the first layer has a first face in directcontact with the current collector substrate and the second layer has asecond face in direct contact with a separator.
 5. The electrode ofclaim 1, wherein the interphase layer comprises a plurality of fluidpassages defined at least in part by the first active material particlesand the second active material particles.
 6. The electrode of claim 5,wherein the plurality of fluid passages are further defined by aplurality of conductive additive particles.
 7. A secondary batterycomprising the electrode of claim
 1. 8. The electrode of claim 1,wherein the electrode is an anode, and the first active materialparticles comprise carbon.
 9. An electrode comprising: a currentcollector substrate; and an active material composite layered onto thesubstrate, wherein the active material composite comprises: a firstlayer including a plurality of first active material particles having afirst distribution of particle sizes; a second layer including aplurality of second active material particles having a seconddistribution of particle sizes; and an interphase layer adhering thefirst layer to the second layer, the interphase layer including anon-planar interpenetration of the first and second layers in whichfirst fingers of the first layer interlock with second fingers of thesecond layer.
 10. The electrode of claim 9, wherein the first fingerseach have a length greater than approximately two microns.
 11. Theelectrode of claim 9, wherein the first layer has a first face in directcontact with the current collector substrate and the second layer has asecond face in direct contact with a separator.
 12. The electrode ofclaim 9, wherein the first layer has a first porosity, the second layerhas a different second porosity, and the interphase layer has a thirdporosity intermediate the first porosity and the second porosity. 13.The electrode of claim 9, wherein the interphase layer comprises aplurality of fluid passages defined at least in part by the firstparticles and the second particles.
 14. A method of manufacturing anelectrode, the method comprising: causing a current collector substrateand an active material composite dispenser to move relative to eachother; and coating at least a portion of the substrate with an activematerial composite, using the dispenser, wherein coating includes:applying a first layer to the substrate using a first orifice of thedispenser, the first layer including a first active material compositeslurry having a plurality of first active material particles and a firstbinder, the first active material particles having a first averageparticle size and a first viscosity; applying a second layer to thefirst layer using a second orifice of the dispenser, the second layerincluding a second active material composite slurry having a pluralityof second active material particles and a second binder, the secondactive material particles having a second average particle size and asecond viscosity; and forming an interphase layer adhering the firstlayer to the second layer, the interphase layer including aninterpenetration of the first and second layers in which first fingersof the first layer interlock with second fingers of the second layer.15. The method of claim 14, wherein the interphase layer has a thirdaverage active material particle size between the first average activematerial particle size and the second average active material particlesize.
 16. The method of claim 14, wherein causing the substrate and thedispenser to move relative to each other comprises moving the substrateusing a backup roll.
 17. The method of claim 14, wherein the dispensercomprises a dual chamber slot die coating head, such that the firstorifice is a first slot of the coating head and the second orifice is asecond slot of the coating head.
 18. The method of claim 14, wherein thefirst viscosity and the second viscosity differ by at least one hundredcentipoise (cP).
 19. The method of claim 14, further comprising:calendering the electrode by pressing the combined first and secondlayers against the substrate, such that an electrode density isincreased in a non-uniform manner, the first layer having a firstporosity and the second layer having a second porosity less than thefirst porosity.
 20. The method of claim 19, wherein the electrodeincludes exactly one crust layer.